Author: marina02

ISA disease management – a holistic approach using surveillance and epidemiological assessment

Introduction: Fish health management programmes are meant to prevent spread of infectious agents. Successful management begins with prevention of disease. Several factors such as biosecurity, genetics, robustness of fish, handling procedures, vaccination efficacy and environmental factors play an important role in prevention. Fish are vulnerable to pathogens and stress due to variations in the biophysical parameters when cultured in open pens at sea resulting in disease outbreak. Some viral diseases in fish are listed by the European Union and fall under the category for eradication or strict control. Infectious salmon anaemia (ISA), a serious viral disease in Atlantic salmon (Salmo salar L.), is caused by an Orthomyxovirus. The pathogenic form is characterised by a deletion in the hyperpolymorphic region (HPR) of segment 6 (ISAV HPRdel). Infection with ISAV HPRdel is listed by EU and notifiable in Norway. When ISA is diagnosed, in most cases, all the fish on a site are stamped out or slaughtered.

Methods: In June 2021, ISA was diagnosed at a site with Atlantic salmon shortly after sea transfer. The fish were vaccinated against ISAV. To build knowledge about disease development in vaccinated fish and risk of virus transmission, the Norwegian Food Safety Authority granted permission to continue production instead of stamping out under close monitoring. A holistic approach was employed to understand disease development using bimonthly fish inspection, analysis of samples (tissues and swabs) collected from healthy and sick fish and water from the net pens and well boat as well as molecular epidemiology, including several historical virus isolates from the region.

Results: ISA-virus was detected more frequently in samples from moribund fish than healthy fish, and was most prevalent in skin swabs compared with gill swabs followed by heart tissue – an aspect that should be taken into consideration when choosing fish and which samples to collect for earliest possible detection. At the start of the study fish from three of seven net pens were positive, while towards the end of the production cycle, all seven were positive for ISAV. Sequencing several historical and recent isolates from the region indicated that ISAV HPR0 probably have undergone independent deletions resulting in several ISAV HPRdel isolates, each giving ISA at different sites.

A broad perspective about movement of fish across the regions, distance between fish farms and possible virus reservoirs in the region need to be carefully assessed for optimal disease management.

1. PATEL, SONAL, NORWEGIAN VETERINARY INSITUTE, Presenter
2. Dale, Ole B, NORWEGIAN VETERINARY INSITUTE, Author
3. Fjellsøy, Kay Roger, Åkerblå, Author
4. Bekkeli, Karl Erik, Salaks, Author
5. Breck, Olav, Norwegian Food SAfety Authorities, Author
6. Bendiktsen, Rune, Salaks, Author
7. Bornø, Geir, NORWEGIAN VETERINARY INSITUTE, Author
8. Brun, Edgar, NORWEGIAN VETERINARY INSITUTE, Author
9. Jørgensen, Lars Gaute, Pharmaq part of Zoetis, Author
10. Hellberg, Hege, Pharmaq Analytiq, Author
11. Larsen, Siw, NORWEGIAN VETERINARY INSITUTE, Author
12. Kvalvik, Henriette, NORWEGIAN VETERINARY INSITUTE, Author
13. Moldal, Torfinn, NORWEGIAN VETERINARY INSITUTE, Author

Why aquaculture needs immunology

Introduction

Health of farmed fish and shellfish deserves a top priority. To help prevent and fight the global disease crisis in aquaculture, it is high time to further explore immunology. And high time for immunologists specialised in aquaculture to start taking aquaculture more seriously. I will discuss the effort that should be put into practical means to maintain health of individuals, by developing functional feeds, and vaccines. These two approaches rely on complementary parts of the immune system to maintain the health of farmed animals. If we agree that infectious diseases are a main cause of the global disease crisis in aquaculture, and can agree on a common aim to prevent rather than cure, future aquaculture needs to build stronger on knowledge of animal physiology. As part of this necessary development, it is high time for aquaculture to further explore immunology.

Methodology

This presentation is based on my experience and personal opinion. I will list how to – to my opinion – not interpret immune responses and what not to measure, and will also list how to correctly interpret immune responses in aquaculture.

Results and Conclusion

Safeguarding good health by prevention is better than cure, so exploit both innate and adaptive immune responses by developing functional feeds, and vaccines. There is no physiological restriction to vaccinating all fish species in aquaculture. Already, Atlantic salmon are routinely vaccinated by injection with polyvalent vaccines. Thus, convince the pharmaceutical industry to invest in finding immune-based correlates of protection, and convince them to do so not only for salmon. Immunostimulation may help establish innate immune priming, and may even lead to a broad protection for periods longer than just a few days. Polysaccharides like beta-glucans, for example, have been around long enough to convincingly show positive effects on fish health. Thus, convince the feed industry to invest in finding immune-based correlates of protection after provision of neutraceuticals. And convince the feed industry to also target invertebrates (e.g. shrimp) in aquaculture. After all, the innate immune systems of not only fish, but also of shrimps and bivalves can be boosted by immunostimulants. Finally, the only sustainable way forward in aquaculture is based on a collective wish to not just reduce mortalities of stocked populations, but maintain the health and welfare of farmed individuals.

1. WIEGERTJES, GEERT, WAGENINGEN UNIVERSITY, Presenter

Investigating the dynamics of parasites infecting Magallana gigas and closely associated invertebrates dominating oyster beds in the Gulf of Biscay

Investigating how climate change will impact the dynamics of pathogens in coastal environments stands pivotal to the One Health perspective of the UN Oceans Decade. In this work, we explore parasites present in wild populations of cupped oysters, Magallana gigas, of the Gulf of Biscay. In addition to oysters (n=694), amphipods (n=327) and polychaetes (n=221), which are ubiquitous in these benthic ecosystems, were also studied in five differently anthropogenically impacted locations. Sampling was carried out bimonthly over one year in the small touristic/fishing village of Plentzia and twice, pre- and post-spawning (May, September), in the other sites; these, included harbours (Pasaia, Arcachon) an oyster farm (La Tremblade) and a Biosphere’s reserve (Mundaka). Sampled organisms were transversally dissected and fixed for histological analysis, with the remaining tissue being frozen for later molecular analyses. The histopathological screening allowed the observation of a number of metazoan, protist, fungal and bacterial parasites, as well as inclusions suggesting the presence of viruses. Tissular and cellular lesions, including infiltration and necrosis, were also documented. In general, amphipods hosted a greater number of protist symbionts (Ciliophora, Apicomplexa, Microsporidia, Ascetosporea) and in higher prevalences than polychaetes and oysters. However, bacterial, viral and fungal infections were only detected in the later. While parasites infecting amphipods showed clear seasonal dynamics, with prevalences peaking during summer, the distribution of parasites in M. gigas appeared rather site-dependent. Oysters from the Plentzia estuary displayed higher prevalences of metazoans (Mytilicolidae, Pinnotheridae), ciliates (Trichodina sp., Sphenophyra sp., Ancistrocoma sp.), bacteria (Rickettsia-like) and viruses (Papilloma-like) than its open sea counterparts. Generally, a higher diversity of parasites was observed in estuarine oysters (Plentzia, Mundaka) than in those from harbours, which hosted less symbionts but with higher prevalences. Even so, histopathological lesions, including necrosis, infiltration and nuclei with marginalized chromatin, were more common in oysters from ports than in those inhabiting less anthropized environments. Complementary molecular analyses are ongoing in order to characterize more accurately some of the parasites observed in this study. By integrating sites with a different temperature gradient and diverse anthropogenic pressures along the Gulf of Biscay, our results provide new insights into the exploration of the impact of global change on the dynamics of marine invertebrate-infecting parasites.

1. Urrutia, Ander, Ifremer, Presenter
2. Akter, Zishan, University of the Basque Country, Author
3. Carnicero, Miren, University of the Basque Country, Author
4. Chollet, Bruno, Ifremer, Author
5. Garcia, Celine, Ifremer, Author
6. Arzul, Isabelle, Ifremer, Author
7. Marigómez, Ionan, University of the Basque Country, Author

clinical presentation and pathological effects of a hydrozoan bloom on farmed atlantic salmon

Introduction

Gelatinous plankton blooms, though largely unpredictable, are an increasing concern for the rapidly growing mariculture industry. In July 2023, a bloom of the colonial hydrozoan Apolemia sp. was first detected in mid-Norway through the citizen science platform Nye.dugnadforhavet.no. By November, the bloom had spread along the entire 2,500 km Norwegian coastline, significantly disrupting aquaculture operations nationwide. In this report, we document the clinical signs and pathological findings observed in farmed Atlantic salmon (Salmo salar) affected by this unprecedented Apolemia sp. bloom at the Austevoll research station of the Institute of Marine Research in Norway.

Methodology

Following reports of increased morbidity and mortality in Atlantic salmon cages at the Austevoll Research Station (IMR), coinciding with a hydrozoan bloom, affected fish were collected for comprehensive analysis. Clinical assessments were performed to document macroscopic external symptoms, while histopathological examinations of the skin, gills, and eyes were conducted to identify and assess the extent of tissue damage. Plasma samples were collected, analyzed for selected biomarkers, and compared to established reference values. Fish behavior was monitored both at the surface and underwater using cameras equipped with remote-controlled pan and tilt functionality. Wound progression was tracked and scored automatically through camera-based detection systems. Daily mortality, expressed as a percentage of stocked fish, was recorded throughout the observation period.

Results and Conclusions.

Soon after the arrival of Apolemia sp., many fish exhibited reduced swimming ability and erratic behavior. In the following days, numerous individuals developed lesions on the eyes and skin, and daily mortality in some cages exceeded 17%. Histopathological examinations of moribund fish revealed acute gill damage, secondary complications such as necrosis and bacterial infections, and the presence of ongoing amoebic gill disease (AGD). Blood biomarker analyses indicated severe physiological stress and signs of organ dysfunction. Due to serious welfare concerns, all affected fish at the site were ultimately euthanized—a measure also taken at several other Norwegian salmon farms impacted by the bloom. These events underscore the urgent need for improved monitoring systems and mitigation strategies to safeguard farmed fish from such environmental hazards. The 2023 bloom in Norway highlights the vulnerability of aquaculture to gelatinous plankton outbreaks and reinforces the importance of continued research and innovation in developing effective management practices.

1. MADARO, ANGELICO, institute of marine research, Presenter
2. Sandlund, Nina, institute of marine research, Author
3. Oldham, Tina Marie Weier, institute of marine research, Author
4. Folkedal, Ole, institute of marine research, Author
5. Nilsson, Jonatan, institute of marine research, Author
6. Stien, Lars Helge, institute of marine research, Author

Camera-based reading of group ID with estimation of individual fish outcomes; an innovation for field trials in large-scale salmon net pens

We present the main results from a project focused on developing and evaluating a new method for conducting randomised field trials in commercial salmon farming using camera technology and automatic sampling with no handling of fish. The primary objective was to create and assess a platform for continuous data collection and assignment of individual fish data to either the test (marked) or the control (unmarked) group. The so-called “IFelt” project used a block-randomised cohabitant design, where treated and untreated fish were placed together into two sea cages. Treated fish were adipose fin-clipped and exposed to a probiotic bath (Stembiont Vital) at time of vaccination. Automated group assignment and continuous estimation of biological parameters such as weight, external wounds, and mobile or adult female salmon lice were performed using Optoscale (underwater camera), and Baader (processing camera with recording of weight, length and quality at harvest).

Validation of group assignment

We collected a total of 404 000 observations from the sea period and data from 289 000 fishes recorded individually at harvest. Daily recordings at sea were 1000 – 2000 fishes per cage albeit with periodic variation. Both camera systems demonstrated high accuracy in group identification. The Optoscale technology achieved 99.9% specificity and 94.6% sensitivity in detecting marked fish. The Baader technology showed similarly high specificity.

Results

During the seawater rearing phase, no significant differences in growth were seen between the treatment groups. The occurrence of external wounds was moderate and did not differ between the groups. However a lower level of mobile and especially of adult female lice was found in the treated group. At harvest, 11–15% spinal deformities was found in the control group, that negatively affected production (weight) and quality. This was likely caused by topping-up the control group with fish from another population that came from a different population. In hindsight, this incomplete randomisation introduced confounding that, interestingly, remained undiscovered until processing of the harvest data.

Discussion and conclusion

The iFelt project demonstrated that advanced camera technology and automated data collection enable precise group assignment based on adipose fin marking, with corresponding estimation of outcome parameters in individual fish being recorded throughout sea production and at harvest. The methodology represents a major leap for future evaluation of biological interventions under industrial field conditions.

1. Midtlyng, Paul J., Aquamedic AS, Presenter
2. Blomsoe, Audhild, Optoscale AS, Author
3. Fylling, Anne Bakke, Previwo AS, Author
4. Lauritzen, Daniel Engen, Sinkaberg AS, Author
5. Skjerve, Eystein, Salmalytics AS, Author
6. Aunsmo, Arnfinn, Salmalytics AS, Author

Immune response of Mytilus sp. challenged with low-virulence and high-virulence isolates of Francisella halioticida

Introduction

In France and other European countries, several hypotheses are currently being explored to explain the recurrent mass mortality events observed in mussels since 2014. Two of these hypotheses involve bacterial species: Vibrio splendidus, known pathogen of aquatic species and Francisella halioticida, pathogen of abalone and Yesso scallop. Our previous studies led to the isolation of several F. halioticida strains. Virulence assessment revealed that some isolates were significantly more virulent than others under the same environmental conditions. In mussels, few pathogens are capable of inducing significant mortality at concentrations below 10⁵ CFU/mL—F. halioticida is one of them. The main objective of this study was to investigate the immune response of hemocytes and gill tissues in the hybrid Mytilus edulis x Mytilus galloprovincialis following infection with F. halioticida.

Methodology

Adult mussels were injected with either the low-virulence isolate FR21, the high-virulence isolate FR22c, or sterile broth (control) at a high concentration (10⁶ CFU/mL). Samples from the haemolymph and gills were collected before injection (T0 control), at 24 hours (T1), and at 72 hours (T2) post-injection for gill tissue only. RNA was extracted using the conventional TRIzol method and sequenced via Illumina technology. A de novo transcriptome was produced using all samples from gills, followed by a differential expression analysis. Proteins and peptides were extracted in parallel and analysed by mass spectrometry for identification.

Results

As expected, survival was significantly compromised in individuals infected with FR22c up to 72 hours post-injection, while mussels injected with FR21 exhibited fewer signs of distress (e.g., shell gaping) after 35–48 hours. Transcriptomic analyses revealed a broadly similar gene expression profile at 24 hours in mussels injected with either FR21 or FR22c. Although fewer transcripts were identified in gill samples, the same immune-related genes were regulated in both conditions. At 72 hours, only gill samples were analysed. Mussels infected with FR21 showed expression patterns trending back toward control levels, whereas individuals exposed to FR22c maintained a strong upregulation of immune-related genes.

Conclusions

This study provides new insights into the immune response of Mytilus sp. to the emerging pathogen F. halioticida. The combined use of transcriptomic and proteomic approaches validated the de novo transcriptome and shed light on the host’s immune response strategies. Further studies incorporating different environmental conditions and additional time points are necessary to deepen our understanding of host–pathogen interactions in this system.

1. BOURAS, Helene, University of Caen Normandy, Marine Ecosystems and oRganisms research Laboratory (MERSEA), Esplanade de la Paix, 14032 Caen, Fra, Presenter
2. CORRE, Erwan, CNRS, Sorbonne Université, FR2424, ABiMS-IFB, Station Biologique, Roscoff, France, Author
3. BERNAY, Benoit, UNIVERSITY OF CAEN NORMANDY, Author
4. BLIN, Jean-Louis, Synergie Mer et Littoral (SMEL), Zone Conchylicole, Blainville‐sur‐mer, France, Author
5. SAVARY, Manuel, Comité Régional de Conchyliculture (CRC) Normandie-Mer du Nord, 35 rue du littoral, 50560 Gouville-sur-Mer, France, Author
6. HOUSSIN, Maryline, LABÉO Frank Duncombe, 1 Route de Rosel, 14053 Caen Cedex 4, France, Author
7. ZATYLNY-GAUDIN, Céline, University of Caen Normandy, Marine Ecosystems and oRganisms research Laboratory (MERSEA), Esplanade de la Paix, 14032 Caen, Fra, Author

Impact of global warming on host/pathogen interactions in a Novirhabdovirus / Rainbow trout (Oncorhynchus mykiss) model

Context :

The development of aquaculture, the world’s fastest-growing agricultural sector, faces several challenges such as global warming, environmental pollution and the emergence of pathogens; impacting the health and welfare of both farm and wildlife animals. Climate modeling projections indicate that global surface temperatures of continents and surface waters (oceans and rivers) could rise by 0.4 to 2.6°C by 2050 according to the UN. Chronic exposure to increased water temperatures constitutes a strong physiological/metabolic stress, likely to alter fish immune responses and resilience to infectious diseases. In addition, the emergence of naturally thermo-adapted viral strains could represent a serious epidemic threat.

Objectives :

In a collaborative project, INRAE and ANSES characterized the impact of rising water temperatures on host pathogen interactions studying 1/ fish health (zootechnics, immune competences) and 2/ virus plasticity focusing on two salmonid viruses with a broad host spectrum and high evolutionary potential, viral hemorrhagic septicemia virus (VHSV) and infectious hematopoietic necrosis virus (IHNV).

Methods :

Twelve field strains of IHNV and VHSV were selected to represent the genetic diversity of viruses circulating worldwide. The in vitro characterization of their temperature sensitivity was initially conducted by assessing their replication kinetics and cytopathic effect at four temperatures ranging from 14 °C to 24 °C in carp and trout cells lines. Based on these results, three strains of each virus were further selected for in vivo investigations of pathogen virulence at different thermal regimes, ranging from zebrafish larvae (3R-compliant) to target species, in accordance with European animal welfare guidelines.

Results and discussion :

Our results demonstrate 1/ the existence of different thermo-sensitivity profiles depending on the viral strains both in vitro and in vivo, 2/ temperature dependent replication kinetics that are transposable from cells to fish, 3/ the appearance of clinical signs in zebrafish larvae characteristic of novirhabdovirus diseases in rainbow trout. Analyses of virus-induced immune responses are ongoing (in cells and zebrafish larvae). Finally, pathogenic strains capable of replicating beyond 24 °C will be selected to study their virulence in rainbow trout and better anticipate the emergence of epidemics.

1. GOURHANNIC, ELISE, INRAE, Presenter
2. FAUVET, Calvin, INRAE, Author
3. MEHRAZ, Manon, INRAE, Author
4. GRIPPON, Pauline, ANSES, Author
5. FRETAUD, Maxence, INRAE, Author
6. BIACCHESI, Stéphane, INRAE, Author
7. MILLET, Jean, INRAE, Author
8. LOUBOUTIN, Lénaïg, ANSES, Author
9. RIGAUDEAU, Dimitri, INRAE, Author
10. MORIN, Thierry, ANSES, Author
11. LANGEVIN, Christelle, INRAE, Author

3D HISTOPATHOLOGY: ADVANCING DISEASE DETECTION IN AQUACULTURE THROUGH TISSUE CLEARING, WHOLE-FISH IMAGING AND AI

Introduction Aquaculture faces various challenges that hinder its development and sustainability, particularly in disease management. Early detection of diseases is essential to reduce intervention periods and improve surveillance programs, which rely on advanced diagnostic tools. Histopathology, a commonly used untargeted method to identify biomarkers (anatomical changes) of infectious and environmental diseases, is limited by the need for highly trained experts. To overcome these constraints, tissue clearing methods, combined with advanced 3D imaging technologies and AI-guided pattern recognition, present unprecedented opportunities for novel diagnostic approaches in fish pathology.

Methodology Our study aims to generate a high-resolution imaging dataset based on 3D imaging of rainbow trout for applications in veterinary medicine. We focus on fingerlings, a developmental stage highly vulnerable to infectious diseases. The fish undergo fixation and tissue clearing before being imaged using advanced lightsheet 3D microscopy. Classical histology is performed in parallel to validate findings with known histological disease markers. Initial acquisitions were conducted on rainbow trout fingerlings infected with the salmonid novirhabdovirus Infectious Hematopoietic Necrosis Virus or mock-infected, imaged in 3D with the open-source MesoSPIM lightSheet microscope. To automate pathological pattern recognition and detection, artificial intelligence (AI) is employed, with a particular focus on the vascular network (VN). By leveraging blood autofluorescence as a label-free diagnostic approach, our method enables identification of VN abnormalities that are not easily detectable by the human eye. Since AI models require large training datasets, we propose a strategy for developing AI systems at the patch scale—small subcubes of data extracted from entire fish volumes.

Results and Perspectives 3D fluorescence imaging of entire cleared rainbow trout fingerlings has been successfully achieved (for infected and mock infected conditions). As a proof of concept, we defined a 1x1x1 mm patch (mesoscopic scale), estimated from the diameter of an arteriole/venule (100 µm), with the objective of detecting around 10 vessels. This project will enable AI-assisted diagnosis of fish pathology by identifying and categorizing 3D patterns for disease recognition. Its unbiased approach will allow differentiation between infectious and naïve groups. By integrating expertise in fish infectiology, imaging, pathology, and deep learning, this interdisciplinary collaboration fosters innovation across multiple fields, including aquatic health, biotechnology, AI, and data science.

1. LANGEVIN, CHRISTELLE, Université Paris-Saclay, INRAE, Presenter
2. Frétaud, Maxence, Université Paris-Saclay, INRAE, Author
3. Mehraz, Manon, Université Paris-Saclay, INRAE, Author
4. Rigaudeau, Dimitri, Université Paris-Saclay, INRAE, Author
5. Rousselot, Sebastien, Université Paris-Saclay, ENS Paris-Saclay, CNRS, Author
6. Perronet, Karen, Université Paris-Saclay, ENS Paris-Saclay, CNRS, Author
7. Marquier, François, Université Paris-Saclay, ENS Paris-Saclay, CNRS, Author
8. Larcher, Thibaut, INRAE, Oniris, Author
9. Rousseau, David, Université d’Angers, Author

A new draft genome of the protozoan parasite Bonamia ostreae, a major pathogen of the flat oyster Ostrea edulis.

The flat oyster (Ostrea edulis) is a native European species that has experienced a dramatic decline towards functional extinction in many regions of the Northeast Atlantic. This decline has been attributed to several factors, including overexploitation and diseases including bonamiosis caused by the intracellular protozoan parasite Bonamia ostreae. This parasite is of major concern and is subject to regulation in the European Union and worldwide. Despite its importance, genomic resources for B. ostreae are extremely limited.

Due to the intracellular nature of B. ostreae and its inability to be cultured in vitro, obtaining high quality -omic data has proven to be particularly challenging. In this study, we applied a targeted parasite isolation protocol combined with specialised bioinformatics pipelines designed to handle complex metagenomic data. This approach enabled the enrichment and assembly of the parasite genome from infected oyster tissues.

Using this integrated methodology, we successfully generated a new high quality genome assembly of B. ostreae. The quality of the assembly was validated by coverage and completeness metrics along with contamination assessments. The genome is 12.35 Mb in length, consists of 78 scaffolds and codes for 5145 protein-coding genes. This genome represents a significant advance in our understanding of this uncultivable marine haplosporidian and provides a fundamental resource for future research.

The availability of a high-quality B. ostreae genome opens up new opportunities to study the biology, evolution, and host-parasite interactions of this important pathogen. In addition, these genomic insights will facilitate the development of more specific and sensitive diagnostic tools, which are critical for the surveillance and management of bonamiosis in Ostrea edulis populations.

1. CHEVIGNON, GERMAIN, IFREMER, Presenter
2. LECADET, CYRIELLE, IFREMER, Author
3. DOTTO-MAUREL, AURELIE, IFREMER, Author
4. SUARD, RAPHAEL, IFREMER, Author
5. ARZUL, ISABELLE, IFREMER, Author

changing waters, changing parasites: temperature-driven shifts in myxozoan life cycles

parasites are integral to biodiversity and serve as an indicator for ecological stability, yet their role is often overlooked in conservation efforts. as we face the sixth mass extinction, parasites are not exempt. myxozoans require two hosts – a vertebrate (fish) and an invertebrate – to complete their life cycle, making them vulnerable to changes in host availability, distribution, and environmental conditions like water temperature. to predict which myxozoan species may decline or emerge in the next decade, we conducted a study that integrated laboratory research with an extensive review of existing literature.

we performed an experimental trial using the myxozoan sphaerospora molnari in common carp (cyprinus carpio), quantifying blood stages in infected fish held at 7, 12, 17, 22, and 27°c, over a 92-day period, to better understand the temperature-related dynamics of proliferation. we also analyzed specific antibody production in the fish to assess how temperature affects the development of adaptive immune responses. additionally, a comprehensive literature review incorporated both laboratory and field studies in myxozoan model species. data related to temperature effects on parasite prevalence, development, life stages, transmission patterns, combined with physiological preference and immunocompetence data from their hosts was used to estimate how predicted temperature will affect myxozoans.

in s. molnari, higher temperatures accelerated parasite proliferation onset (variation between 14 days at 27°c and 91 days at 7°c), but did not affect the duration of proliferation. peak parasite density in the blood was observed at 17°c, with up to threefold lower levels at higher temperatures. antisera analyses indicated the antibodies are not formed during the 92-day experiment, in fish held at 7 or 12 °c, but we demonstrated the production of increasing numbers of specific antibodies over time, with increasing temperatures.

our findings on s. molnari show that the enhanced host’s immune responses, thanks to the common carp’s tolerance for elevated water temperatures, ultimately curbs parasite proliferation. this pattern differs markedly from parasites like tetracapsuloides bryosalmonae and ceratonova shasta, which infect salmonids with narrow thermal tolerance. in those cases, warming induces severe physiological stress and intense parasitosis due to partially impaired host immunity. for enteromyxum leei in gilthead seabream, higher temperatures increase both infection prevalence and host antibody production, often leading to parasite clearance from gut tissues. these species-specific patterns underscore the complex relationship between temperature, parasite biology, and host immunity, highlighting that the emergence of disease is closely tied to the host’s optimal physiological range.

1. Schwegler, Hella L., Fish Health Division, University of Veterinary Medicine, Veterinärplatz 1, 1210 Vienna, Austria, Presenter
2. Sneha, Patra, Czech Globe, Global Change Research Institute, Czech Academy of Sciences, Bělidla 4a, 60300 Brno, Czech Republic, Author
3. Holzer, Astrid S., Fish Health Division, University of Veterinary Medicine, Veterinärplatz 1, 1210 Vienna, Austria, Author